I had a similar problem with my then brand new Chevy crewcab dually. Factory pads lasted 7,000 mi (yeah, I'm hard on brakes, but not THAT hard). After much complaining, the dealership replaced them with identical factory pads - those lasted EXACTLY 7,000 miles again.

At that point I just started doing the brakes myself with NAPA severe duty pads and the mileage is SIGNIFICANTLY better. The problem is that the factory pads are purposely designed to be soft to avoid complaints about brake squeaks.